"I welcome Subramanian Swamy in the BJP. I believe this will benefit the party. It's time for a nationalist focus," Rajnath Singh told reporters here while announcing the merger.
Swamy, who was commerce and law minister in the Chandra Shekhar government in the early 1990s, said he was happy over the development.
"I am glad. I have been in the Jan Sangh. I hope to work together with my colleagues," he told reporters after meeting Rajnath Singh at his residence here.
According to Swamy: "The country is passing through difficult times and needs the BJP for resolving the various problems."
Detailing his plans, he said: "I will work for a national purpose so a new future for India can be built. I am looking forward to working towards welfare of India's youth."
Swamy, who is known for his right-wing ideology, had joined the National Democratic Alliance last year when Nitin Gadkari was BJP president. Recently, he had been pursuing a merger of his outfit with the main opposition party.
The move is aimed at strengthening the NDA ahead of 2014 national polls.